The Excretory System
The Excretory Systemhttp://www.youtube.com/watch?v TZMJeZL-BVg&safe active
Introduction Every body activity uses energy andgenerates wastes. If waste products were not removed,they would quickly accumulate inharmful proportions. Some wastes are poisonous andpose a serious threat to health if theyare not removed promptly. The process of getting rid ofmetabolic wastes is called excretion
The chemical composition ofintercellular fluid is for the life of thecells. If it becomes too salty, the cells canbecome dehydrated. If it gets too watery the cells canbloat.
If too much acid or baseaccumulates, the cells' enzymescan stop working. If urea and other wastes collect,the cells can die of poisoning. Homeostatic mechanisms withinthe body keep the chemicalcomposition of the intercellular fluidconstant when conditions change.
Excretion and Homeostasis Excretion aids homeostasis byremoving wastes and regulatingthe salt and water balance. The blood picks up carbondioxide, excess salts, urea,and any excess water thatmay be present and carries themto the excretory organs, whichchannel the wastes out of thebody.
Fortunately, atoms and molecules do not wearout, but may be changed or rearranged andused over and over again. Many of the end products of various cellactivities can be recycled and used in otherprocesses. As a result, the amount of waste that actuallyneeds to be discharged from the body is verysmall in relation to the amount of work done byall the cells of the human body. Several organs take part in human excretion.The lungs, skin, liver, and the transport systemplay important roles; however, the mainexcretory organs are the kidneys.
The Skin the skin is the largest organ of thebody The skin covers an area of 1.5 to 2square meters on an average adult the thickness of the skin varies from0.5mm on the eyelids to 6mm on thesoles of the feet there are 2 general layers of theskin: epidermis and dermis
Epidermis the outer layer is called theepidermis and is made up of layers offlat cells the surface of cells of this layer aredead they are constantly rubbing andbeing replaced by the cells belowthem this outer layer of skin provides awaterproof shield against germs andbacteria
Dermis this layer is under the epidermis the cells in this layer are still alive this layer contains blood vessels,nerve endings, sweat and oilglands, hair follicles, and fat cells the sweat glands have tubes thatlead to the surface of the skin atpoints called sweat pores perspiration is released at thesesweat pores
water urea and inorganic salts areincluded in perspiration besides ridding the body of thesewastes, perspiration also cools thebody and helps maintain a properbody temperature the evaporation of sweat on thesurface of the skin requires heat toturn liquid into gas this heat comes from the body,which results in a cooling of the body
https://kidshealth.org/en/kids/skinmovie.html
The Lungs Gas exchange occurs between the microscopiccapillaries and the alveoli in the lungs Oxygen is diffused into the blood stream from thealveoli into the capillaries Oxygen is attracted to, and held by, the hemoglobinin the red blood cells of the body Oxygen is released into living cells and used incellular respiration- the releasing of energy fromfood and oxygen within the individual cells The waste product from cellular respiration iscarbon dioxide which is diffused out of the celland carried back to the lungs and diffused from thecapillaries into the alveoli and exhaled by the lungs Water vapour is also exhaled during this process
The Liver the liver is located just to right of thestomach sugar (glucose) in the blood is removedin the liver and stored as glycogen when the sugar level in the blood goesdown the liver breaks down the glycogenand releases sugar back into the blood if there is no room for the liver to storeglycogen the liver changes the sugar tofat and stores it in other parts of thebodyhttps://www.youtube.com/watch?v GYFJ8oqNdCE
the liver also removes from our bodiespoisonous substances, such aspoisons in fish, poisonous fumes frompaint, and chemicals sprayed on food the liver is our bodies main defencefrom poisons like those mentionedabove the liver also changes the hemoglobinfrom dead red blood cells into bile,which is used in the small intestine tobreak down fats bacteria from the large intestine isremoved from the body by the liver
The Kidneyshttps://www.youtube.com/watch?v CX kF0bKoTk
The kidneys are the main organs of theexcretory system as they are the body’sfiltration system The kidneys help maintain a balanceamong the elements inside the body-thisbalance is referred to as homeostasis The kidneys perform the followingimportant jobs: They remove urea and other wastesfrom the blood They regulate the amount of water inthe circulatory system They adjust the amounts of certainsubstances in the blood
The kidneys filter wastes andpoisons from the blood at anincredible rate The entire blood supply of the bodypasses through the kidneys onceevery 30 minutes Within each kidney are an estimatedone million microscopic nephronswhere filtering actually takes place Each nephron contains a cluster ofcapillaries known as a glomerulus
A cup shaped sac called a Bowman’scapsule surrounds each glomerulus The blood that flows through theglomerulus is under great pressure This causes water, urea, glucose andminerals into the Bowman’s capsule Red blood cells, white blood cells, andprotein remain in the blood As blood continues through the bloodvessels, it winds around the renaltubule-during this time reabsorptionoccurs
Glucose and chemicals such as potassium,sodium, hydrogen, magnesium, andcalcium are reabsorbed into the blood Almost all of the water removed duringfiltration returns to the blood during thereabsorption phase-the water and mineralcomposition of the body is actuallyregulated in the kidneys The kidneys control the amount of liquidin our bodies Now, only wastes are in the nephrons
These wastes are called urine andinclude water, urea, and inorganicsalts There may also be some sugar andnutrients present if there is an excessof these substances in the blood The cleansed blood goes into the veinsthat carry the blood from the kidneysand into a major vein that carries theblood back to the heart From the heart, the cleansed bloodwill circulate throughout the body
WasteProductAmmoniaOrigin of WasteExcretory OrganProductBreakdown of amino Kidneysacids in the liverUreaConversion ofKidneys, Skinammonia in the liverCarbonDioxideCellular Respiration Lungs(breakdown ofglucose in cells)Cellular Respiration Kidneys, Intestines,(breakdown ofSkin, Lungsglucose in cells)WaterMineralSaltsFood and waterKidneys, Skin
Why is excrement (poop) notincluded in this list of metabolicwastes?Excrement is not a product ofcellular metabolism. It is a leftover after the body absorbswhat nutrients it needs fromthe small intestine.
The Kidney and Bladder:An Overviewhttp://www.youtube.com/watch?v qxb2 d9ilEw
KidneysThe kidneys remove metabolicwastes from the body by filteringthe blood.They work continuously, processingall of the blood in the body every 30minutes.Every 24 hrs they kidneys filterapproximately 200 liters of fluid andreturn to the bloodstream all but 1-2liters, which are excreted as urine.
The Excretory Systemconsists of:2 kidneys: bean-shaped organslying near the back of the abdominalcavity2 ureters: lead from kidney to theurinary bladder1 bladder: lies low in the abdominalcavity1 urethra: extends from the bladderto the exterior of the body, carryingurine though the urogenital organs
The kidney, bean-shaped and about 10cm long, has a dark coloured core whichis densely packed with blood vessels.These vessels form a network ofcapillaries and small tubes known as themedulla.The medulla is divided up into a number oftriangular shaped sections calledpyramids.
Each pyramid consists of arterioles,which branch into smaller and smallerarterioles, the tiniest of which deliversblood to the nephron.Likewise many tiny venules, takingblood away from the nephron jointogether making larger and largervenules, finally making up the renalvein.The pyramid also contains a greatnumber of urine carrying collectingtubules which empty the urine into thecentral cavity, known as the renalpelvis.
The three basic RenalProcesses:1. Filtration – the passage of proteinfree substances through thecapillaries of the glomerulus into theBowman’s Capsule.2. Tubular re-absorption – theremoval of water and useful solutesfrom the filtrate3. Tubular secretion – the addition ofcertain substances to the filtrate
FiltrationBlood is filtered by nephronsEach nephron begins in a renalcorpuscle, composed of a glomerulusenclosed in a Bowman’s CapsuleCells, proteins and other largemolecules are filtered out of theglomerulus by a process of filtration.The filtrate continues on through theproximal tubule all the way throughto the collecting duct to form urine.
Re-absorption Process by which solutes and water areremoved from the tubular fluid (filtrate)and transported to the blood. Two step process:a) Begins with the active or passiveextraction of substances from the filtrateinto the renal interstitium (connectivetissue that surrounds the nephrons)b) Transport of these substances from theinterstitium into the bloodstream Water and solutes such as Na (sodium)are reabsorbed
Tubular SecretionThe cells of the tubules remove certainmolecules and ions from the blood anddeposit these into the fluid within thetubulesTubular secretion of H is important inmaintaining control of the pH of theblood.– When the pH of the blood starts to drop, morehydrogen ions are secreted– If the blood should become too alkaline,secretion of the hydrogen ions is reduced– In maintaining the pH of the blood within itsnormal limits of 7.3-7.4, the kidney canproduce a urine with a pH from 4.5 to 8.5
The NephronThere are 5 parts each with a specific functionin the nephron.The parts of the nephron are as follows(LABEL DIAGRAM):1.Renal Capsule – Ultrafiltration2.Proximal Convoluted Tubule – Reabsorption3.Loop of Henle – Formation of a Salt Bath4.Distal Convoluted Tubule – Homeostasis andSecretion5.Collecting Duct – Concentration controlhttps://www.youtube.com/watch?v 8UVlXX-9x7Qhttps://www.youtube.com/watch?v H2VkW9L5QSU
1. Renal Capsule – Ultrafiltration The renal artery splits into numerous arterioles, each feeding anephron. The arteriole splits into numerous capillaries, which form a knotcalled a glomerulus. The glomerulus is enclosed by the renal capsule (of Bowman’scapsule): the first part of the nephron. The arteriole leading into the glomerulus (afferent arteriole) iswider than the one leading out (efferent arteriole), so there is ahigh blood pressure in the capillaries of the glomerulus. The blood pressure in the capillaries is 60-70 mm Hg, whereaselsewhere in the body capillary pressure is only 25 mm Hg. This pressure forces plasma out of the blood by ultrafiltration. Those substances that do pass from the glomerulus into thecapsule comprise what is called the filtrate. Blood cells and large protein molecules are too big to passthrough the tiny pores in the capsule capillaries. Substances such as salts, sugars, water, wastes are made upof smaller molecules which can pass easily through the poresto enter the capsule.
2. Proximal Convoluted Tubule – Re-absorption Longest (14 mm) and widest part of the nephron. It is lined with epithelial cells containing microvilliand numerous mitochondria. In this part of the nephron over 80% of the filtrateis reabsorbed into the tissue fluid and then to theblood. This ensures that all the “useful” materials thatwere filtered out of the blood (such as glucose andamino acids) are now returned to the blood. All glucose, all amino acids, and most mineralions are reabsorbed by active transport from thefiltrate to the tissue fluid. They then diffuse into theblood capillaries. 80% of the water is reabsorbed to the blood byosmosis.
3. Loop of Henle – Formation of a Salt Bath The job of the loop of Henle is to make the tissue fluid in themedulla hypertonic compared to the filtrate in the nephron. The purpose of this “salt bath” is to reabsorb water. The loop of Henle does this by pumping sodium and chloride ionsout of the filtrate into the tissue fluid. The first part of the loop (the descending loop) is impermeableto ions, but some water leaves by osmosis. This makes the filtrate more concentrated as it descends. The second part of the loop (the ascending loop) contains Na andCl- pumps, so these ions are actively transported out of the filtrateinto the surrounding tissue fluid. Water would follow by osmosis, but it cannot because theascending loop is impermeable to water. Therefore the tissue fluid becomes more salty (hypertonic) andthe filtrate becomes less salty (hypotonic). Since the filtrate is most concentrated at the base of the loop, thetissue fluid is also more concentrated at the base of the medulla.
4. Distal Convoluted Tubule –Homeostasis and Secretion Certain substances are actively transported from theblood into the filtrate, in other words they aresecreted. It is relatively short and has a boarder of microvilliwith numerous membrane pumps for activetransport. The important point about this secretion is that it isregulated by hormones, so this is thehomeostatic part of the kidney. Substances secreted include H (for pHhomeostasis), K (for salt homeostasis), toxins, andother foreign substances.
5. Collecting Duct – Concentration As the collecting duct passes through thehypertonic salt bath in the medulla, waterleaves the filtrate by osmosis, soconcentrating the urine and conserving water. The water leaves through special waterchannels in the cell membrane calledaquaporins. These aquaporin channels are controlled by ahormone called ADH so allowing the amountof water in the urine to be controlled.
The Nephron at Workhttp://www.biologymad.com/resources/kidney.swf
The Role of Kidneys in MaintainingHomeostasisEach drop of blood in your body passesthrough a kidney about 350 times per day.The kidney is able to fine tune the compositionof blood and thereby help maintainhomeostasisKidney failure results in the breakdown ofhomeostasis and death occurs shortly thereafter (approximately 2 weeks).
The kidneys regulate the water content ofthe blood: Human kidneys filter out about half a cup of fluidfrom the blood each minute. Without reabsorption of water you would urinateabout 45 gallons (170.34 litres!!!) of water a day. Reabsorption of water into the blood occurs throughosmosis when the filtrate (fluid which has beenfiltered) travels through the tubule and the collectingduct. Reabsorption is controlled by a negative feedbackmechanism that involves the amount of ADH(antidiuretic hormone) circulating in the blood.This hormone increase the permeability of the distaltubule and the collecting duct to water, allowing morewater to be reabsorbed from the urine.
The release of ADH is regulated by receptor cells inthe hypothalamus (area of the brain). The release ofADH increases water reabsorption and produces urinemore concentrated than the blood. If a person does not have sufficient water, the loweredlevel of water in the blood signals the hypothalamusto release more ADH. The ADH travels through the blood to the body. Uponreaching the kidney tubule it stimulates the cellmembranes to become more permeable to water.As a result more water is reabsorbed into the bloodand the urine becomes more concentrated If a person has too much water less ADH isreleased. Then the cell membranes of the tubulesbecome impermeable to water. They do not allowwater to return to the blood and urine is verydiluted.
Water Regulation by the Kidneyshttp://www.youtube.com/watch?v vB7tSHqR1eY&safe active
THE BLADDER Your bladder is the hollowmuscular organ that collectsand stores urine. As yourbladder fills, it expands tostore the urine. On average, your bladder canhold 400-600 ml of urine forup to about five hours. The muscle in your bladderwall is called the detrusormuscle. The detrusor musclerelaxes to allow your bladderto fill. When you go to thetoilet, it contracts to squeezeout urine.
What would happen if you didn’t drink water?https://www.youtube.com/watch?v 9iMGFqMmUFs
Sphincters associated with Excretion:There are two sphincter mechanisms:The internal sphincter is a ring of muscle that holds the neck of thebladder in place. Your body opens and shuts it automaticallywithout you thinking about it.Internal urethral sphincter: Smooth muscle Involuntary control More superiorly locatedThe external sphincter acts like a tap and keeps urine in thebladder. It is controlled by the pudendal nerve, which is controlledby the voluntary nervous system. This means it’s under yourcontrol - you decide when to let it open. The external sphincter isalso called the distal sphincter.External Urethral sphincter: Skeletal muscle Voluntary control Posteriorly located
How do you know when to empty your bladder? The micturition reflex tells you when you need toempty your bladder. This happens on average four toeight times a day. The reflex is controlled by yourcentral nervous system. When your bladder is about half full, the stretchreceptors in the walls of your bladder become activeand send signals along your pelvic nerves to your spinalcord. A reflex signal is sent back to your bladder, whichmakes the detrusor muscle in the bladder wall contract.The contraction increases the pressure in your bladder,and this is what makes you want to pass urine. Because the external sphincter is under voluntarycontrol, you don’t urinate until you decide to relax thismuscle.http://www.youtube.com/watch?v qMR-rAVlbV0
Homeostasis – Water Balance and UrineConcentrationHomeostatic mechanism involved in regulating levels of materialsin the blood is called negative feedback and involves two veryimportant hormones: Antidiuretic Hormone (ADH), andAldosterone.Antidiuretic hormone (ADH): Maintains water balance in the body. When the hypothalamus in the brain detects a lowering ofwater volume in the body. it signals the pituitary gland to release ADH into thebloodstream ADH increases the reabsorption of water by the kidneys (byincreasing the permeability of the collecting tubules). If too much water is present, the hypothalamus decreases thesecretion of ADH. ADH H2O reabsorption
Aldosterone: Maintains blood pressure in the body. Blood pressure drops when the level ofsodium in the blood falls. Renin, an enzyme produced by the kidneyscauses the adrenal gland to release thehormone aldosterone promotes the reabsorption of sodium Blood vessels constrict, blood pressure rises asa result, ADH is released, and a sensation ofthirst are all part of this process. When blood pressure and sodiumconcentration in the blood returns to normal,renal renin secretion is turned off. Na reabsorption H2O reabsorption
Diuretics:Diuretics increase the output of urine, leavingthe body below normal water levels: Caffeinated Beverages: Such as coffee, teaand Coke all stimulate arteries to contract,which raises blood pressure, and more wateris forced under pressure out of theglomerulus into the nephron for excretion. Alcohol: Inhibits the flow of ADH, thereforenot enough water is reabsorbed in the tubule,and water loss occurs. Drugs: Can act as a diuretic, or an antidiuretic(opposite effects).
How does caffeine keep us awake?https://www.youtube.com/watch?v foLf5Bi9qXs
Characteristics of Urine: about 95% water usually contains urea, uric acid, and creatinine (breakdown product from creatine phosphate used up inmuscles) may contain trace amounts of amino acids and varyingamounts of electrolytes
activities can be recycled and used in other processes. As a result, the amount of waste that actually needs to be discharged from the body is very small in relation to the amount of work done by all the cells of the human body. Several organs take part in human excretion. The lungs, skin, liver, and the transport system
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Reading Essentials Chapter 34 Circulatory, Respiratory, and Excretory Systems 399 . In Chapter 37, you will learn about the lymphatic system, which also is part of the immune system. . excretory systems in this chapter. Chapter 34 Function Organs Disorders Circulatory Respiratory Excretory.
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Excretory System-Training Handout Karen L. Lancour National Rules Committee Chairman – Life Science Excretion -Excretion is the removal of the metabolic wastes of an organism. Wastes that are removed include carbon dioxide, water, salt, urea and uric acid. All excreted wastes travel at some time in the blood. Organs of the Excretory System
